Nestled high in the Indian Himalayas, a tiny body of water has earned a macabre nickname: „Skeleton Lake.“

Officially named Roopkund, the lake’s edges are rimmed with human bones and frozen bodies — some with frozen hair and flesh still attached. Bold hikers have stacked some of the remains into morbid shrines.

On a rare summer day, when parts of the lake melt, more scattered skeletal remains sometimes float to the surface. Researchers have determined that up to 800 people are buried there.

„It’s a small, enclosed space, and there are bones everywhere,“ William Sax, an anthropologist who visited Roopkund in 1978 and consulted on a 2004 National Geographic documentary about the lake, told Business Insider. „It feels scary and disturbing.“

Anthropologists like Sax are interested in the area because nobody knows what killed the people buried there. A forest ranger named Hari Kishan Madhwal came upon the lake in 1942, yet more than 75 years later, researchers are no closer to pinpointing how or why these people perished. The mystery of the lake deepened this summer, when a DNA study of 38 skeletons revealed that people from three genetically distinct groups had died at Roopkund in at least two waves, about 1,000 years apart.

„We expected that this analysis would help resolve the mystery of Roopkund Lake by determining the ancestry of these skeletons,“ Eadaoin Harney, the lead author of that recent study, told Business Insider. „While we did accomplish this goal, I think we have instead revealed that this site is even more mysterious than we ever expected.“

Here’s what it’s like to visit Roopkund, and a few scientists‘ best guesses about what might have happened there.

A remote Himalayan lake holds up to 800 skeletons from people who died 1,000 years apart. The mystery remains unsolved. slides

A remote Himalayan lake holds up to 800 skeletons from people who died 1,000 years apart. The mystery remains unsolved. slides

For the recent analysis, Harney and her team drilled into the femurs and long arm bones of dozens of skeletons from the lake to extract DNA.

They found that of the 38 skeletons examined, 23 had ancestry related to people from present-day India and died between the seventh and 10th centuries, during several events.

Fourteen of the skeletons, meanwhile, were most closely related to people from the Mediterranean islands of Crete and Greece, and one had Southeast Asian ancestry. That group of 15 individuals died between the 17th and 20th centuries, likely in a single event.

Wikimedia Commons

That discovery changed scientists' understanding of Skeleton Lake, since previous research had suggested that most of the bones at the site dated back to the year 800 or so.

Sax said the new data about a second wave of deaths was „a real stunner.“

„The timing of that most recent event — which happened sometime in the last few hundred years — makes it a really interesting puzzle,“ he added.

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Conducting this kind of research at the lake isn't easy. Roopkund, which means "lake of form" in Hindi, is more than 16,500 feet above sea-level.

Spattadar/Wikimedia Commons

The surrounding environs are breathtakingly beautiful, Sax said. The lake is located in India's Nanda Devi National Park.

Abhijeet Rane/Flickr

Still, he added, "there's no reason for anybody to be up there." That's what makes the presence of these skeletons so mysterious.

Anirban Biswas/Flickr

For visitors to the lake, Sax said, the site's macabre history is plainly visible: "You can't take a single step without steeping on bones."

Himadri Sinha Roy

Some travelers have collected the bones and stacked them in piles, out of fascination or perhaps respect. But such human interference disturbs the site, Harney said.

It makes it „quite difficult to perform standard archaeological analyses on these remains,“ she added.

Some tourists reportedly even take bones away from the site as morbid souvenirs.

Himadri Sinha Roy

Myriad explanations have been put forward as to how these individuals perished, from a freak hailstorm to a mass ritual suicide.

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Harney's team thinks it's possible that some people who perished during the first wave of Skeleton Lake deaths experienced "a mass death during a pilgrimage event."

Himadri Sinha Roy

The lake is near a present-day pilgrimage route through the region, the study authors wrote.

Pramod Joglekar

A local folk song even describes a mass pilgrimage to the shrine of a mountain goddess, called Nanda Devi, near the lake.

The study authors said the song is about „a king and queen and their many attendants, who — due to their inappropriate, celebratory behavior — were struck down by the wrath of Nanda Devi.“ The lyrics recount the goddess flinging balls as „hard as iron.“

Atish Waghwase

Those balls of iron could have been hail that rained down during a severe storm, according to the study authors.

Ashokyadav739/Wikimedia Commons

Harney said researchers observed compression fractures on several of the skeletons that might be consistent with injuries from a hailstorm or rockslide.

Sax also recalled that some of the skulls found near the lake appeared to have been cracked open, damaged by blunt objects.

Atish Waghwase

Ultimately, though, Harney is hesitant to speculate about any causes of death, since it's not possible to determine that information through the genetic analysis her team completed.

Since the skeletons date back to multiple different time periods, it’s likely that they died in different ways, she said.

In their analysis, Harney’s team wrote that the findings „refute previous suggestions that the skeletons of Roopkund Lake were deposited in a single catastrophic event.“

Atish Waghwase

Harney and her colleagues' analysis did, however, put to rest a few theories about what could have killed the people at the lake.

These groups probably didn’t die in an epidemic, as a 2004 National Geographic documentary suggested, because the DNA analysis found no evidence of bacterial infection in any of the skeletons.

Battle probably wasn’t the cause either, since the skeletons Harney’s team examined came from 23 males and 15 females, including children and elderly people, and no weapons were found nearby.

Shubhamrathod15/Wikimedia Commons

Kathleen Morrison, an anthropologist at the University of Pennsylvania who was not involved in the recent study, offered one other possible explanation: "When you see a lot of human skeletons, usually it's a graveyard," she told The Atlantic.

„I suspect that they’re aggregated there, that local people put them in the lake,“ she said, noting that it’s unlikely all these people died at the lake’s edge.

Abhijeet Rane/Flickr

But Harney thinks the site is too remote to be a graveyard. "I don't know of any evidence that would support this," she said.

What’s more, Harney’s team analyzed DNA from present-day groups that live in the areas closest to Roopkund, and did not find many genetic similarities between these individuals and the skeletons. That indicates it’s unlikely that a local population once used this site as a burial ground.

Atish Waghwase

Harney said further study of the bones and bodies is needed to figure out how these individuals died.

„I think that there are really two parts to this mystery,“ she said. „The first is, who are these people and why did they go to Roopkund Lake?“

To answer that question, Harney thinks researchers would need to find historical written accounts that describe a journey to Roopkund.

„The second question that I would like to answer is, how did these individuals die?“ she said. „There are a large number of remains still at Roopkund Lake that are yet to be analyzed in any way, so it is possible that in the future we will be better able to answer this question.“